1/(1*3)+1/(3*5)+1/(5*7)+.+1/(49+51)的简便运算

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1/(1*3)+1/(3*5)+1/(5*7)+.+1/(49+51)的简便运算
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1/(1*3)+1/(3*5)+1/(5*7)+.+1/(49+51)的简便运算
1/(1*3)+1/(3*5)+1/(5*7)+.+1/(49+51)的简便运算

1/(1*3)+1/(3*5)+1/(5*7)+.+1/(49+51)的简便运算
1/(1*3)+1/(3*5)+1/(5*7)+.+1/(49*51)
=(1-1/3+1/3-1/5+1/5-1/7+.+1/49-1/51)/2
=(1-1/51)/2
=25/51

1/2[2/(1*3)+2/(3*5+2/(5*7)+......+2/(49*51))]
=1/2[1/1-1/3+1/3-1/5+1/5-1/7+......+1/49-1/50]
=1/2[1-1/50]=(1/2)*(49/50)=49/100
思路说明:观察每项的分母的两个因数(1、3;3、5;5、7;......;49、50)之间差都是2,如果折解为两个因数的倒...

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1/2[2/(1*3)+2/(3*5+2/(5*7)+......+2/(49*51))]
=1/2[1/1-1/3+1/3-1/5+1/5-1/7+......+1/49-1/50]
=1/2[1-1/50]=(1/2)*(49/50)=49/100
思路说明:观察每项的分母的两个因数(1、3;3、5;5、7;......;49、50)之间差都是2,如果折解为两个因数的倒数的因式差,则为1/1-1/3=2/1*3; 1/3-1/5=2/3*5; 1/5-1/7=2/5*7;....;1/49-1/50=2/49*50, 这样整个序列算式的就无形中扩大了2倍,所以要在拆解式的前面再乘个二分之一(1/2)

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